Improved method of operating a heated draw pin with synthetic yarns



Dec. 18, 1962 TIN-YAM AU 3,058,530

IMPROVED METHOD OF OPERATING A HEATED DRAW PIN WITH SYNTHETIC YARNS Original Filed Aug. 28. 1958 INVENTOR TIN YAM AU ATTORNEY 3,068,530 IMPRGVED METHQD F OPERATlNG A HEATED DRAW PIN WITH SYNTHETIC YARNS Tin-Yam Au, Holiday Hills, Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del, a corporation of Delaware Continuation of application Ser. No. 757,741, Aug. 28, 1958. This application Nov. 3, 1960, Ser. No. 68,327 1 Claim. (Cl. 18-48) This invention relates to an improved method for drawing filamentary structures composed of synthetic linear polymers. This application is a continuation of co-pending application Serial No. 757,741 filed August 28, 1958, now abandoned.

Commercial production of synthetic linear polymeric yarns, filaments, and the like customarily involve drawing the filaments to an increased length, thereby producing a structure of greater tenacity having characteristic X-ray diffraction patterns indicative of internal orientation along the filament axis. Drawing may be carried out at any temperature below the softening point of the polymer, hence the process is often termed cold drawing. This operation is carried out on most melt-spun and other thermo-plastic materials, and the invention to be described herein-below is therefore applicable to all of these, and particularly applicable to fiberforming polyamides and polyesters.

The drawing operation is normally accomplished by drawing the filamentary structure between drawing rolls, as is well known. This drawing is usually localized on or about a drawing element, in order that controlled and reasonably unvarying conditions of temperature and tension (snubbing) may be maintained during drawing, thereby aiding the proper orientation and attenuation of the filaments. The drawing surface may be that of a flat or curved plate, a pin, or a cylindrical surface, such as a pipe. The drawing surface should be carefully prepared; the so-called matte finish is usually preferred.

A pipe is a frequently preferred drawing element. It is easily maintained at a given surface temperature by internal electrical or fluid-transfer heating. Varying the number of helical or circumferential yarn wraps about the pipe controls the tension during drawing as well as the contact time on the element.

Many filaments are of themselves somewhat abrasive in nature. Moreover, it is an accepted practice to add to such structures abrasive pigments or fillers, e.g., titanium dioxide is frequently employed to deluster or otherwise change certain properties of a filament. Therefore, the drawing surface in time becomes scored, abraded, and worn due to contact with the running filaments. Further, there is a tendency for excess lubricant (finish) from the filaments to accumulate on the drawing surface, forming a gummy film which prevents uniform drawing. Finally, at elevated temperatures, there occurs a gradual buildup of non-volatile organic material, inorganic material and other extraneous matter, the combined accumulation of which forms a diiiicultly removable infusible deposit which interferes with drawing uniformity and operability in that such deposits, will cause an excessive number of broken filaments in the yarn treated.

Any one of the above-mentioned difiiculties causes a change in the surface properties of the drawing element, and eventually the drawing surface must be refinished. When the drawing element is a pipe, only a relatively small fraction of its available surface becomes worn or is subject to the accumulation of extraneous material. Nevertheless, restorative steps are required at about the same frequency as for pins and plates, negating thereby many of the advantages of the pipe as a drawing element.

States Patent O An object of this invention is to provide an improved process for drawing filamentary structures utilizing the major portion of a cylindrical surface, disposed between the drawing means, as a drawing element.

A further object is to provide a process for drawing filaments wherein the abrasive effects of the filamentary structures being drawn are minimized.

A still further object is to provide a process for drawing filaments wherein the accumulation of foreign matter on the drawing element is avoided and wherein the quality and uniformity of the yarn treated are maintained at high levels.

Yet another object of this invention is to prolong the useful life of a cylindrical drawing element. These and other objects, together with-the means for accomplishing these objects, will appear hereinafter.

According to this invention, there is provided a rotatable drawing element situated between any well-known means for drawing filamentary structures, such as draw rolls and the like.

The process of this invention comprises drawing filamentary structures over a drawing element, which is rotated, preferably a pipe, the axis of which is inclined at an angle to the direction of an incoming filamentary structure. Such rotation of the drawing surface does not affect the operability of the process or the quality of the product adversely. Actually the rotation as hereafter discussed prevents build-up of undesired deposits on the pip surface, maintains high yarn quality and permits wear to be distributed evenly over the major portion of the pipe surface.

The FIGURE illustrates a preferredembodiment of this invention. Yarn 1 is fed over feed roll 2, driven by means of the drive shaft 3 of a motor (not shown), past draw pin 4, around a first draw roll 5 (driven by a motor-not shown, then around the cylindrical drawing element 6, from which it is passed around a second draw roll (not shown). Drawing element 6 is mounted rotatably between the top bearing linkage 9 and the worm drive assembly 7 mounted on frame8.

The pipe may be rotated continuously in one direction, it may be rotated intermittently in one direction, or it may rotate back and forth in a continuous fashion. This latter method is particularly applicable to heated pipes in which a liquid or gaseous heat-transfer agent is employed. Continuous or intermittent unidirectional rotation is feasible for unheated pipes or for heated pipes in which electrical heating is employed. Preferably, the pipe is rotated continuously at less than about one revolution per minute about its own-longitudinal axis in the direction counter to the direction of yarn travel. Surprisingly, when such a pipe is inclined at an angle to the direction of yarn travel, and when the yarn encounters the pipe near the bottom and leaves near the top, such a clock-wise-counter-clockwise relationship between the directions of pipe rotation and yarn travel creates a most eificient sweeping action which serves to prevent the undesirable accumulation of foreign matter on the pipe surface. Conversely, where yarn passes from the top to the bottom of a vertically inclined pipe, and the pipe is rotated in the same direction as the yarn travel, undesirable accumulations are likewise continuously removed from the pipe surface when a clockwise-clockwise relationship obtains for the directions of pipe rotation and yarn travel.

The increase in useful pipe life due to the practice of this invention has been found to be proportional to the ratio of pipe diameter to the width of the filament band being drawn thereon. For example, in the case of an 840 denier, filament yarn drawn on a 1% inch diameter rotating pipe r.p.m.), at a drawing speed of 2500 yards per minute, useful pipe life is increased 17 times over that of a similar pipe held stationary, over which similar yarn is drawn. Where the said yarn is drawn on a 3 /2 inch diameter pipe, the useful pipe life is increased 48 times over that of asimilar stationary pipe. When a 210 denier, 34 filament yarn is drawn on the same 3 /2 inch diameter pipe, the useful pipe life is 290 times greater than that of a similar stationary pipe, over which similar yarn is drawn. The increase in useful pipe life is independent of pipe length or number of yarn wraps on the pipe surface where the helix angle of the yarn with respect to the pipe remains constant.

The rate of pipe rotationshould be slow, relative to the filament drawing speed, that is, the filament being drawn should be moving about the pipe at a rate faster than the pipe surface is moving. When such a relationship exists, the filaments are confronted with an essentially stationary drawing surface, and are, accordingly, drawn in a uniform and reproducible manner. Since drawing on a commercial scale is carried out as rapidily as possible, maintaining a rate of pipe rotation less than about one revolution per minute is ordinarily sufiicient. Much higher rates of rotation are possible in any particular application, so long as drawing operability and yarn quality are not adversely affected.

The rotated pipe may be heated, either electrically or by the use of fluid or gaseous heat-transfer media. When heated electrically, the interior of the pipe contains the necessary heating elements, and the pipe mounting means should include provision for maintaining electrical contact while the pipe rotates. Such means are readily available. When the heating is accomplished by a fluid transfer, the interior-of the pipe contains the conduits, etc. necessary for maintaining adequate fluid circulation. For these applications, the pipe mounting means should include provision for sealingiand insulating, as well as an inlet and outlet for circulating the heating fluid. Such means are also readily available, although it is preferred in many applications to provide stationary connections, and to rotate the pipe back and forth in an oscillating manner. Actual rotation of the pipe, whether continuous or intermittent, unidirectional or oscillatory, is accomplished by well-kncwn-applications of familiar apparatus.

The present invention has utility in a variety of applications. The rotating pipe can be used for drawing filaments under a wide variety of conditions of temperature and tension, and for extended periods of time. It is particularly useful in the second and subsequent stages of a multi-stage drawing operation, since such drawing is usually carried out at elevated temperatures. The rotating pipe may be used to preheat filaments preparatory to twisting or crimping operations, or may be employed to dry the said filaments.

Many advantages derive from the practice of this ine The drawing ur a e i snt w s a d fi ament positioning on the pipe remains constant during rotation to provide a constant drawing profile (the temperature and tension relationship between the drawing element and the structure being drawn).

Use of the rotating drawing element of this invention permits yarn quality, yarn physical properties, and process operability to remain at a consistently high level for much longer periods of time. By avoiding conditions of wear and reducing the amount of extraneous material accumulated over the drawing surface, the heat transfer characteristics of the pipe and the coefficient of friction between the yarn and the pipe remain uniform. Accordingly, after operating for a considerable length of time, the quality of the yarn drawn on the rotating drawing element is substantially better than that of the yarn drawn over a stationary drawing element.

These advantages are achieved with a minimum of additional investment, since the cost of frequent resurfacing of the pipe exceeds the cost of the means necessary to rotate the pipe.

Iclaim:

An improved process for reducing and evenly distributing wear, maintaining substantially constant heat exchange characteristics, and maintaining substantially constant frictional characteristics on the single continuous peripheral surface of a heated cylindrical draw element used in constant tension drawing and heat treating moving filamentary structures of synthetic polymeric material during the drawing and heat treating operation, said process consisting of the steps of rotatably supporting and maintaining the axis of the draw element in a fixed position in space at such an angle with respect to the direction of said moving filamentary structure while a plurality of turns thereof are in engagement around said element, supplying heat to said element and through said element to said'structure, and rotating the draw element independently of filamentary structure movement at such a speed and more than a predetermined extent with respect to the linear speed and angle of the filamentary structure that the line of contact between the structure and the element is shifted over the peripheral surface during heat treatment of the moving filamentary structure to cause the entire engaged portion of the surface of the element to be efiectively cleared of extraneous matter by sweeping action of the structure over and with respect to the element surface while maintaining the filamentary structure in a state of constant tension.

7 References Cited in the file of this patent 'UNITED STATES PATENTS 2,289,232 Babcock July 7, 1942 2,778,058 Gabler Jan. 22, 1957 2,874,410 Kinney Feb. 24, 1959 

